Solute-enhanced production of gamma-valerolactone (GVL) from aqueous solutions of levulinic acid

ABSTRACT

A method to produce levulinic acid (LA) and gamma-valerolactone (GVL) from biomass-derived cellulose or lignocellulose by selective extraction of LA using GVL and optionally converting the LA so isolated into GVL, with no purifications steps required to yield the GVL.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of co-pending application Ser. No.13/115,420, filed May 25, 2011, the contents of which are incorporatedherein by reference.

FEDERAL FUNDING STATEMENT

This invention was made with government support under DE-FC02-07ER64494awarded by the US Department of Energy and W911NF-09-2-0010 awarded bythe ARMY/ARO. The government has certain rights in the invention.

BACKGROUND

Significant advances have been made in recent years with respect tousing heterogeneous catalysts for converting biomass-derived compoundsto fuels and chemicals. Conventional approaches deconstruct solidcellulose into smaller molecules that are soluble in various solvents(e.g., water, ionic liquids), thereby allowing transport of thesereactants to the active sites on the heterogeneous catalyst, themajority of which are located within the pores of a high-surface areamaterial. A difficulty in implementing this strategy is that chemicalcomponents used to deconstruct solid cellulose (e.g., sulfuric acid) mayalter the performance of heterogeneous catalysts used subsequently toconvert the soluble biomass-derived reactants to the desired fuelsand/or chemicals. As a result, costly purification steps are required toimplement a cascade catalytic process. Thus, the present methodaddresses a long-felt and unmet need by providing a route to levulinicacid and gamma-valerolactone that uses gamma-valerolactone itself as anextraction solvent to extract levulinic acid from an aqueous solution.

In short, there is an increasing need for methods to produce fuels andchemicals from renewable, domestic sources to reduce the dependence onthe fossil sources of carbon. A great many processes have been reportedin the literature; however, scale-up of these processes to industrialscale has been severely hampered due to the necessity of purifying thefinal products and/or intermediates. Purification is often required toavoid negatively impacting downstream catalytic processes. Levulinicacid, for example, is a building block that can be upgraded tovalue-added chemicals and liquid transportation fuels by severalpathways. Levulinic acid, however, is conventionally produced bycellulose deconstruction using dilute solutions of mineral acids. Themineral acid needs to be removed prior to downstream processes, such ashydrogenation to gamma-valerolactone (GVL). If the acid is not removed,the downstream reactions are severely impacted or rendered infeasible.

In co-pending and co-owned application Ser. No. 13/115,420 is describeda strategy that uses alkylphenols as a solvent for a biphasicextraction. Alkylphenols are insoluble in water, and thus separate fromaqueous solutions of the cellulose deconstruction feed, while alsoextracting a portion of the levulinic acid. Even though alkylphenolextraction has significant advantages over previous processes, there arestill some drawbacks. It uses an external solvent, requires finalpurification of the product by distillation, and has a moderatepartition coefficient: approximately 2 for levulinic acid (concentrationof levulinic acid in the organic phase divided by the concentration oflevulinic acid in the aqueous phase). Also, the partition coefficientfor formic acid (a co-product in the production of levulinic acid fromcellulose) is less than 0.2. Thus, in the earlier process, formic acidcannot be used as internal source of H₂.

SUMMARY OF THE INVENTION

Making fuels and chemicals from biomass is complicated by the need toseparate and to purify the intermediate platform molecules at highyields. Conventional approaches to making useful chemicals from biomasstypically require very difficult and economically unfeasible separationand purification steps. Disclosed herein is a method in which levulinicacid (LA) (from any source, but preferably produced from biomass) isisolated from an aqueous reaction solution using an extraction solventthat comprises, consists essentially of, or consist ofgamma-valerolactone.

Thus, described herein is a method to isolate levulinic acid (LA). Oneversion of the method comprises providing an aqueous solution comprisingLA and a sufficient concentration of a water-soluble solute to yield asolution that is substantially immiscible with gamma-valerolactone. TheLA is then extracted from the aqueous reaction solution using anextraction solvent comprising GVL.

It is preferred, but not required that the aqueous solution of LA isacidic. The reaction solution can be acidified using any acid. Preferredacids are mineral acids and organic acids, for example (and notlimitation): solid acids, hydrochloric acid, nitric acid, phosphoricacid, sulfuric acid, boric acid, hydrofluoric acid, trifluoroaceticacid, hydrobromic acid, acetic acid, oxalic acid, toluenesulfonic acid,and the like.

The water-soluble solute is added to the aqueous reaction solution toensure that a biphasic system is created between the aqueous reactionlayer and GVL. The solute is preferably a water-soluble salt,monosaccharide, disaccharide, or trisaccharide. Preferred solutesinclude sodium chloride and fructose. If the solute is sodium chloride,it is preferred to be at a concentration of from about 6 wt % to about35 wt % (i.e. saturated), based on the weight of the water in theaqueous solution.

A particular advantage of the method is that all or a portion of theextracted LA can be converted into GVL and the GVL so formed can berecycled back into the process for use as the extraction solvent.Converting the LA into GVL can be accomplished in the presence of acatalyst comprising one or more metals from Groups 6-14 of the periodicchart. Preferred metals include, but are not limited to, ruthenium,nickel, platinum, rhodium, tin, copper, and combinations thereof.Ruthenium, tin and combination thereof are most preferred. Also, apreferred route from LA to GVL is to convert the LA into a LA ester andthen to reduce the LA ester to GVL. The final reduction to GVL mayoptionally take place in the presence of a metal oxide or metal complexcatalyst.

In another version of the method, the aqueous solution comprising LA isproduced by deconstructing cellulose, hemicellulose, glucose, xylose, orcombinations and/or oligomers thereof in an aqueous, acidic reactionsolution, to yield an aqueous solution comprising LA or an aqueoussolution comprising LA and fufural. To that solution of LA and/or LA andfurfural is added a sufficient concentration of a water-soluble soluteto yield a solution that is substantially immiscible withgamma-valerolactone. The LA is then extracted from the aqueous reactionsolution using an extraction solvent comprising GVL. In this version ofthe method, the deconstruction step may take place in a biphasic systemhaving a first phase and a second phase, wherein the first phasecomprises the aqueous, acidic reaction solution and the second phasecomprises GVL, and wherein the first and second phases are substantiallyimmiscible (as noted earlier). In this approach, the LA is formed in thedeconstruction reaction in the aqueous phase and simultaneouslyextracted into the substantially immiscible phase comprising GVL.

Yet another version of the method is specifically to makegamma-valerolactone (GVL) by providing an aqueous solution comprisinglevulinic acid (LA) and a sufficient concentration of a water-solublesolute to yield a solution that is substantially immiscible withgamma-valerolactone (GVL). The LA is extracted from the aqueous solutionusing an extraction solvent comprising GVL. All or a portion of theextracted LA is then converted to GVL. At least a portion of the GVL soformed can be recycled for use in the extraction step.

The entire method may be conducted in batch fashion or continuously. TheLA extracted may be the final product, or the GVL formed from the LA.Additionally, either the LA or the GVL may be used as a platformchemical to make other downstream products, such as butene.

Hydrogenating the LA into GVL can be accomplished in a number of ways.Preferably the hydrogenation takes place in the presence of a catalystcomprising one or more metals from Groups 6-14 of the periodic table,more preferably still a catalyst comprising ruthenium, nickel, platinum,palladium, rhodium, tin, copper, chromium and combinations thereof, andmost preferably a catalyst comprising ruthenium and tin. Thehydrogenation of LA to GVL may also be accomplished by hydrogen transferusing homogeneous or solid oxide catalysts in the presence of anH-donor, such as an alcohol. In transfer hydrogenation, higher yieldscan be achieved by first converting the LA into a LA ester (by acidcatalyzed reaction with an alcohol or an olefin) and then reducing theLA ester to GVL by transfer hydrogenation. Preferably, the LA ester isreduced to GVL in the presence of a solid oxide catalyst.

Thus the entire route to yield GVL proceeds by deconstructing biomass inan aqueous solution using an acid catalyst (homogeneous orheterogeneous) to yield LA, extracting the LA from the aqueous solutionusing an extraction solvent comprising GVL, and hydrogenating the LA soextracted into GVL.

A distinct advantage of the method is that the GVL product is stableduring the hydrogenation of LA. Thus, it is possible to increase the GVLconcentration in the product mix by successive cycles of cellulosedeconstruction, LA extraction, and LA hydrogenation to GVL. Byaccumulating a large concentration of GVL in the product mix, GVL can beeasily (and cost-effectively) separated from aqueous reaction solutionvia extraction.

The overall strategy disclosed herein is to convert lignocellulosicbiomass to value-added fuels and chemicals by partially removing oxygento yield reactive intermediates (denoted herein as platform molecules,such as LA, GVL, and others). The platform molecules are valuable anduseful commercial products. The platform molecules can be converted intoany number of desired final products, including liquid transportationfuels. As a general proposition, platform molecules have fewerfunctional groups as compared to the carbohydrates found naturally inbiomass (e.g., xylose, glucose). Because there are less reactivefunctional groups, the platform molecules can be selectively upgraded toother useful chemicals via catalytic upgrading processes.

Another advantage of this strategy is that the lower degrees offunctionality and boiling points of these platform molecules allow forcatalytic processing in the vapor phase and/or in organic solvents. Thisalleviates the need to develop heterogeneous catalysts that are stableunder more demanding hydro-thermal reaction conditions. One suchplatform molecule is levulinic acid (LA) (3, 4) from which a variety offuels and chemicals can be made, such as valeric acid esters (5),methyltetrahydrofuran (6-8), and esters and ketals of LA (9). Anotherbuilding block from the reduction of LA is gamma-valerolactone (GVL)(10, 11), which can be used directly as a fuel additive (12), or as aprecursor for fuels (13) and chemicals (14, 15). While LA can be formedin significant yields (>50%) by cellulose deconstruction in aqueoussolutions of mineral acids such as sulfuric acid (SA) (16, 17), achallenge for profitable, large-scale production of LA and itsderivatives has been separating the LA from the mineral acid used in theprocess. This is necessary so that the LA can be further processeddownstream without the negative effects of the mineral acid (18).

As illustrated schematically in FIG. 1, AP solvents can be used toselectively extract LA from aqueous solutions after a cellulosedeconstruction step. In addition, AP solvents extract GVL from waterwith a higher partition coefficient (the concentration of the solute inthe organic phase divided by the concentration of the solute in theaqueous phase) compared to LA. Accordingly, the GVL concentration in theAP solvent can be increased by the conversion of LA to GVL, combinedwith the recycle of this stream for successive extractions. Importantly,a preferred carbon-supported RuSn catalyst (20, 21) can be used toselectively reduce LA to GVL by hydrogenation in the presence of AP,without hydrogenation of the solvent. This is a critical discovery inthat it enables the aforementioned recycling strategy for enhancing theGVL concentration. This then enables the easy and cost-efficientrecovery of the GVL from the AP solvent by simple distillation. Afterdistillation of GVL from the organic phase, the aqueous phase containingany residual LA and possibly acid (after extraction with the AP solvent)can be recycled for subsequent cycles of cellulose deconstruction,providing an effective strategy for managing the acid used in thedeconstruction of the incoming biomass. There are several distinctadvantages to the present approach as compared to conventionalapproaches for making GVL. Notably, the GVL can be recovered by simpleextraction without having to evaporate water—or any other solvent forthat matter. Only the product itself is evaporated (and only if a verypure GVL product stream is required).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram depicting use of AP solvents to separateand purify LA from aqueous solutions which may contain a homogenous acidcatalyst (sulfuric acid is shown).

FIG. 1B is a schematic diagram depicting the use of AP solvents toproduce, separate, and purify GVL from aqueous solutions of levulinicacid potentially containing homogeneous acids (sulfuric acid is shown).The process depicted can be used for deconstructing cellulose fromlignocellulosic biomass.

FIG. 1C is a schematic diagram depicting the conversion of LA to GVL byhydrogen transfer using butyl levinulate (BL) as the intermediate.

FIG. 2A is a graph depicting GVL reaction rate versus time-on-stream fordifferent feeds of LA. Ru—Sn/C, weight hourly space velocity (WHSV)=1.2h⁻¹, 493 K 35 bar (H₂). In the graph, simulated feed (sim.) was changedto feed prepared from cellulose, then back to simulated feed, and thenswitched to a feed prepared from corn stover.

FIG. 2B is a graph depicting GVL reaction rate versus time-on-stream fordifferent feeds of LA. The conditions were the same as described forFIG. 2A. The simulated feed was changed to a feed prepared frompre-treated corn stover, then switched back to simulated feed.

FIG. 3 is a graph depicting GVL production rate versus time on stream at493 K and 35 bar (H₂). Feed composition is 2 M LA and 2 M FA in SBP witha WHSV of 1.6 for Ru—Sn/C (▪) and 2.9 h⁻¹ for Ru/C (●).

FIG. 4 is a graph depicting LA conversion versus time on stream at 493 Kand 35 bar (H₂). Feed composition is 2 M LA and 2 M FA in SBP with aWHSV of 1.6 h⁻¹ for Ru—Sn/C (▪) and 2.9 h⁻¹ for Ru/C (●).

FIG. 5: Energy ratio (defined as percentage of GVL low combustionenergy) used in the reboiler versus the number of stages in theseparation by distillation of GVL from AP at 1 bar. Feed concentrationof GVL: 2.5 M in SBP (▪), 0.5 M in SBP (●), 2.5 M in PTAP (□), 0.5 M GVLin PTAP (◯), and 2.5 M in SBP at 0.1 bar (♦).

FIG. 6: Energy ratio (defined as percentage of GVL low combustionenergy) versus number of stages in the separation by distillation of GVLfrom AP at 1 bar. Feed composition of GVL into distillation column: 0.46M in SBP (▪), 0.75 M in SBP (●), 1.01 M in SBP (♦), 1.44 M in SBP (▾),and 2.5 M in SBP (□).

FIG. 7: Schematic diagram illustrating a process for salt-enhancedproduction of GVL from aqueous solutions of levulinic and formic acidsas disclosed herein.

FIG. 8: Graph depicting the conversion rate of levulinic acid to GVL(primary axis, ♦) and formic acid to CO₂ (secondary axis, ▪) over RuSnat 453 K versus time-on-stream.

FIG. 9: Graph depicting the conversion rate of levulinic acid to GVLover RuSn at 453 K versus time-on-stream. The feed was neutralized priorto reaction.

DETAILED DESCRIPTION

Abbreviations and Definitions

AP=alkylphenol. As used herein, an alkylphenol is defined as a compoundhaving the formula:

wherein R¹-R⁵ are independently selected from the group consisting ofhydrogen, hydroxyl, esters, ethers, carboxylic acids, and C₁-C₂₄ linear,branched, or cyclic alkyl or alkene, provided that at least one of R¹-R⁵is alkyl. All positional isomers (ortho, meta, para) are explicitlyincluded, as are compounds having more than one hydroxy group, e.g.,alkyl-substituted-1,4-dihydroxybenzene. Mono- and di-alkylphenols arepreferred, as are APs wherein the alkyl substituent(s) is a C₁-C₁₂linear, branched, or cyclic alkyl, more preferably still a C₁ to C₆linear or branched alkyl.

BL=butyl levinulate.

“Biomass” as used herein includes materials containing cellulose,hemicellulose, lignin, protein and carbohydrates such as starch andsugar. Common forms of biomass include trees, shrubs and grasses, cornand corn husks as well as municipal solid waste, waste paper and yardwaste. Biomass high in starch, sugar or protein such as corn, grains,fruits and vegetables, is usually consumed as food. Conversely, biomasshigh in cellulose, hemicellulose and lignin is not readily digestible byhumans and is primarily utilized for wood and paper products, fuel, oris discarded as waste. “Biomass” as used herein explicitly includesbranches, bushes, canes, corn and corn husks, energy crops, forests,fruits, flowers, grains, grasses, herbaceous crops, leaves, bark,needles, logs, roots, saplings, short rotation woody crops, shrubs,switch grasses, trees, vegetables, vines, hard and soft woods. Inaddition, biomass includes organic waste materials generated fromagricultural processes including farming and forestry activities,specifically including forestry wood waste. “Biomass” includes virginbiomass and/or non-virgin biomass such as agricultural biomass,commercial organics, construction and demolition debris, municipal solidwaste, waste paper, and yard waste. Municipal solid waste generallyincludes garbage, trash, rubbish, refuse and offal that is normallydisposed of by the occupants of residential dwelling units and bybusiness, industrial and commercial establishments, including but notlimited to: paper and cardboard, plastics, food scraps, scrap wood, sawdust, and the like.

FA=formic acid. FID=flame ionization detector. GVL=γ-valerolactone.HPLC=high-performance liquid chromatography.

As used herein, the term “hydrogenation catalyst” refers withoutlimitation to any catalyst, now known or developed in the future,homogenous or heterogeneous, that catalyzes the hydrogenation ofcarbonyl bonds (C═O). Preferred catalysts will reduce carbonyl bondspreferentially versus carbon-carbon double bonds (C═C). The activitiesneed not be exclusive, but the chosen catalyst should catalyze thehydrogenation of C═O bonds at a rate much larger than the catalystcatalyzes the hydrogenation of C═C bonds. Catalysts comprising one ormore metals from Groups 6-14 are preferred, also these metals doped withgallium, boron, germanium, indium and/or tin. Ruthenium, nickel,platinum copper, chromium and rhodium (alone, in combination, alloyedwith other metals, and/or doped with gallium, germanium, indium and/ortin) are preferred. Other hydrogenation catalysts may also be used, suchas metal hydrides (e.g., NaBH₄), polyoxometalates, Raney Ni, Raney Cu,etc. The catalysts may be used with or without a support.

Selective reduction may also be accomplished by transfer hydrogenationusing a hydrogen donor. The term “hydrogen donor” refers to any compoundwith the ability to transfer a hydrogen atom to other substance.Exemplary hydrogen donors which can be utilized include, but are notlimited to primary and secondary alcohols, polyols, olefins,cycloalkenes, carboxylic acids, and esters.

The rate of H-transfer can be increased by using homogeneous orheterogeneous catalysts. Exemplary catalysts include, but are notlimited to, metals, zeolites, metal oxides supported or unsupported suchas MgO, ZrO₂, gamma-Al₂O₃, CeO₂, CeZrO_(x), MgOAl₂O₃, Mg/Al/ZrO_(x),MgO/SiO₂, CeO₂ZnO, Sn-beta-zeolite, Ti-beta-zeolite, Sn-containingmesoporous silica, as well as metal salts and complexes of Pd, Pt, Ru,Ir, Rh, Fe, Ni, Co, Os, Mo. A full list of suitable hydrogen donors andcatalysts can be found in R. A. W Johnsotne & A. H Wilby (1985)“Heterogeneous catalytic transfer hydrogenation and its relation toother methods for reduction of organic compounds,” Chem. Rev. 85:129-170, which is incorporated herein by reference.

IPA=isopropyl alcohol. LA=levulinic acid. Mineral acid=anymineral-containing acid, including (by way of example and notlimitation), hydrochloric acid, nitric acid, phosphoric acid, sulfuricacid, boric acid, hydrofluoric acid, hydrobromic acid, and the like.MTHF=methyltetrahydrofuran. Organic acid=any organic acid, withoutlimitation, such as toluensulfonic acid, formic acid, acetic acid,trifluoroacetic acid, oxalic acid, and the like. SA=sulfuric acid.SBP=sec-butyl phenol.

Lewis Acid/Base=A Lewis acid is defined herein as any chemical speciesthat is an electron-pair acceptor, i.e., any chemical species that iscapable of receiving an electron pair, without limitation. A Lewis baseis defined herein as any chemical species that is an electron-pairdonor, that is, any chemical species that is capable of donating anelectron pair, without limitation.

In preferred versions of the invention, the Lewis acid (also referred toas the Lewis acid catalyst) may be any Lewis acid based on transitionmetals, lathanoid metals, and metals from Group 4, 5, 13, 14 and 15 ofthe periodic table of the elements, including boron, aluminum, gallium,indium, titanium, zirconium, tin, vanadium, arsenic, antimony, bismuth,lanthanum, dysprosium, and ytterbium. One skilled in the art willrecognize that some elements are better suited in the practice of themethod. Illustrative examples include AlCl₃, (alkyl)AlCl₂, (C₂H₅)₂AlCl,(C₂H₅)₃Al₂Cl₃, BF₃, SnCl₄ and TiCl₄.

The Group 4, 5 and 14 Lewis acids generally are designated by theformula MX₄; wherein M is Group 4, 5, or 14 metal, and X is a halogenindependently selected from the group consisting of fluorine, chlorine,bromine, and iodine, preferably chlorine. X may also be a psuedohalogen.Non-limiting examples include titanium tetrachloride, titaniumtetrabromide, vanadium tetrachloride, tin tetrachloride and zirconiumtetrachloride. The Group 4, 5, or 14 Lewis acids may also contain morethan one type of halogen. Non-limiting examples include titanium bromidetrichloride, titanium dibromide dichloride, vanadium bromidetrichloride, and tin chloride trifluoride.

Group 4, 5 and 14 Lewis acids useful in the method may also have thegeneral formula MR_(n)X_(4-n); wherein M is Group 4, 5, or 14 metal;wherein R is a monovalent hydrocarbon radical selected from the groupconsisting of C₁ to C₁₂ alkyl, aryl, arylalkyl, alkylaryl and cycloalkylradicals; wherein n is an integer from 0 to 4; and wherein X is ahalogen independently selected from the group consisting of fluorine,chlorine, bromine, and iodine, preferably chlorine. X may also be apsuedohalogen. Non-limiting examples include benzyltitanium trichloride,dibenzyltitanium dichloride, benzylzirconium trichloride,dibenzylzirconium dibromide, methyltitanium trichloride,dimethyltitanium difluoride, dimethyltin dichloride and phenylvanadiumtrichloride.

Group 4, 5 and 14 Lewis acids useful in method may also have the generalformula M(RO)_(n)R′_(m)X_((m+n)); wherein M is Group 4, 5, or 14 metal;RO is a monovalent hydrocarboxy radical selected from the groupconsisting of C₁ to C₃₀ alkoxy, aryloxy, arylalkoxy, alkylaryloxyradicals; R′ is a monovalent hydrocarbon radical selected from the groupconsisting of C₁ to C₁₂ alkyl, aryl, arylalkyl, alkylaryl and cycloalkylradicals; n is an integer from 0 to 4; m is an integer from 0 to 4 suchthat the sum of n and m is not more than 4; and X is a halogenindependently selected from the group consisting of fluorine, chlorine,bromine, and iodine, preferably chlorine. X may also be a psuedohalogen.Non-limiting examples include methoxytitanium trichloride,n-butoxytitanium trichloride, di(isopropoxy)titanium dichloride,phenoxytitanium tribromide, phenylmethoxyzirconium trifluoride, methylmethoxytitanium dichloride, methyl methoxytin dichloride and benzylisopropoxyvanadium dichloride.

Group 5 Lewis acids may also have the general formula MOX₃; wherein M isa Group 5 metal; X is a halogen independently selected from the groupconsisting of fluorine, chlorine, bromine, and iodine, preferablychlorine. A non-limiting example is vanadium oxytrichloride.

The Group 13 Lewis acids have the general formula MX₃; wherein M is aGroup 13 metal and X is a halogen independently selected from the groupconsisting of fluorine, chlorine, bromine, and iodine, preferablychlorine. X may also be a psuedohalogen. Non-limiting examples includealuminum trichloride, boron trifluoride, gallium trichloride, indiumtrifluoride, and the like.

The Group 13 Lewis acids useful in method may also have the generalformula: MR_(n)X_(3-n) wherein M is a Group 13 metal; R is a monovalenthydrocarbon radical selected from the group consisting of C₁ to C₁₂alkyl, aryl, arylalkyl, alkylaryl and cycloalkyl radicals; and n is annumber from 0 to 3; and X is a halogen independently selected from thegroup consisting of fluorine, chlorine, bromine, and iodine, preferablychlorine. X may also be a psuedohalogen. Non-limiting examples includeethylaluminum dichloride, methylaluminum dichloride, benzylaluminumdichloride, isobutylgallium dichloride, diethylaluminum chloride,dimethylaluminum chloride, ethylaluminum sesquichloride, methylaluminumsesquichloride, trimethylaluminum and triethylaluminum.

Group 13 Lewis acids useful in this disclosure may also have the generalformula M(RO)_(n)R′_(m)X_(3-(m+n)); wherein M is a Group 13 metal; RO isa monovalent hydrocarboxy radical selected from the group consisting ofC₁ to C₃₀ alkoxy, aryloxy, arylalkoxy, alkylaryloxy radicals; R′ is amonovalent hydrocarbon radical selected from the group consisting of C₁to C₁₂ alkyl, aryl, arylalkyl, alkylaryl and cycloalkyl radicals; n is anumber from 0 to 3; m is an number from 0 to 3 such that the sum of nand m is not more than 3; and X is a halogen independently selected fromthe group consisting of fluorine, chlorine, bromine, and iodine,preferably chlorine. X may also be a psuedohalogen. Non-limitingexamples include methoxyaluminum dichloride, ethoxyaluminum dichloride,2,6-di-tert-butylphenoxyaluminum dichloride, methoxy methylaluminumchloride, 2,6-di-tert-butylphenoxy methylaluminum chloride,isopropoxygallium dichloride and phenoxy methylindium fluoride.

Group 13 Lewis acids useful in this disclosure may also have the generalformula M(RC(O)O)_(n)R′_(m)X_(3-(m+n)); wherein M is a Group 13 metal;RC(O)O is a monovalent hydrocarbacyl radical selected from the groupconsisting of C₂ to C₃₀ alkacyloxy, arylacyloxy, arylalkylacyloxy,alkylarylacyloxy radicals; R′ is a monovalent hydrocarbon radicalselected from the group consisting of C₁ to C₁₂ alkyl, aryl, arylalkyl,alkylaryl and cycloalkyl radicals; n is a number from 0 to 3 and m is anumber from 0 to 3 such that the sum of n and m is not more than 3; andX is a halogen independently selected from the group consisting offluorine, chlorine, bromine, and iodine, preferably chlorine. X may alsobe a psuedohalogen. Non-limiting examples include acetoxyaluminumdichloride, benzoyloxyaluminum dibromide, benzoyloxygallium difluoride,methyl acetoxyaluminum chloride, and isopropoyloxyindium trichloride.

The most preferred Lewis acids for use in the method are metal halidesgenerally and more specifically transition metal halides, lathanoidmetal halides, and Group 5, 13, and 14 metal halides. Preferred amongthe metal halides are metal chlorides. Preferred transition metalchlorides include, but are not limited to, TiCl₄, VCl₃. and the like.Preferred Group 13 and 14 metal halides and chlorides include, but arenot limited to, BF₃, AlCl₃, SCl₄, InCl₃, and GaCl₃. Preferred lanthanoidchlorides include, but are not limited to, LaCl₃, DyCl₃ and YbCl₃.

Mono-, di- and trisaccharides=a monosaccharide is a carbohydrate havingthe general formula C_(X)(H₂O)_(y), where x and y are integers from 3 toabout 8. Monosaccharides are classified by the number of carbon atomsthey contain: diose (2) triose (3) tetrose (4), pentose (5), hexose (6),heptose (7), etc. Disaccharides and trisaccharides are dimmers andtrimers, respectively, of monosaccharides.

A “solid acid catalyst” can comprise one or more solid acid materials.The solid acid catalyst can be used independently or alternatively canbe utilized in combination with one or more mineral acid or other typesof catalysts. Exemplary solid acid catalysts which can be utilizedinclude, but are not limited to, heteropoly acids, acid resin-typecatalysts, meso-porous silicas, acid clays, sulfated zirconia, molecularsieve materials, zeolites, and acidic material on a thermo-stablesupport. Where an acidic material is provided on a thermo-stablesupport, the thermo-stable support can include for example, one or moreof silica, tin oxide, niobia, zirconia, titania, carbon, alpha-alumina,and the like. The oxides themselves (e.g., ZrO₂, SnO₂, TiO₂, etc.) whichmay optionally be doped with additional acid groups such as SO₄ may alsobe used as solid acid catalysts.

Further examples of solid acid catalysts include strongly acidic ionexchangers such as cross-linked polystyrene containing sulfonic acidgroups. For example, the Amberlyst®-brand resins are functionalizedstyrene-divinylbenzene copolymers with different surface properties andporosities. The functional group is generally of the sulfonic acid type.The Amberlyst®-brand resins are supplied as gellular or macro-reticularspherical beads. (Amberlyst® is a registered trademark of the DowChemical Co.) Similarly, Nafion®-brand resins are sulfonatedtetrafluoroethylene-based fluoropolymer-copolymers which are solid acidcatalysts. Nafion® is a registered trademark of E.I. du Pont de Nemours& Co.)

Zeolites may also be used as solid acid catalysts. Of these, H-typezeolites are generally preferred, for example zeolites in the mordenitegroup or fine-pored zeolites such as zeolites X, Y and L, e.g.,mordenite, erionite, chabazite, or faujasite. Also suitable areultrastable zeolites in the faujasite group which have beendealuminated.

TCD=thermal conductivity detector. WHSV=weight hour space velocity.XRD=X-ray diffraction.

Numerical ranges as used herein are intended to include every number andsubset of numbers contained within that range, whether specificallydisclosed or not. Further, these numerical ranges should be construed asproviding support for a claim directed to any number or subset ofnumbers in that range. For example, a disclosure of from 1 to 10 shouldbe construed as supporting a range of from 2 to 8, from 3 to 7, 5, 6,from 1 to 9, from 3.6 to 4.6, from 3.5 to 9.9, and so forth.

All references to singular characteristics or limitations shall includethe corresponding plural characteristic or limitation, and vice-versa,unless otherwise specified or clearly implied to the contrary by thecontext in which the reference is made.

The processes described herein can be run in batch mode, semi-continuousmode, and/or continuous mode, all of which are explicitly includedherein.

All combinations of method or process steps as used herein can beperformed in any order, unless otherwise specified or clearly implied tothe contrary by the context in which the referenced combination is made.

The methods described and claimed herein can comprise, consist of, orconsist essentially of the essential elements and limitations of thedisclosed methods, as well as any additional or optional ingredients,components, or limitations described herein or otherwise useful insynthetic organic chemistry.

Biomass to Levulinic Acid:

The inventive method to yield levulinic acid (LA) is schematicallydepicted in FIG. 1A. Here, a biomass feedstock 8, such aslignocellulose, cellulose, etc. is introduced into a reaction vessel 10containing an acidic aqueous solution. The solution is preferablyacidified with a mineral acid, but any acid will do, including organicor solid acids. High temperature, compressed water also demonstratesacidity and can produce LA without externally supplied acids, so long asit degrades/deconstructs the cellulose found in the feedstock 8 to yieldLA. The digested, aqueous solution, which contains LA and may containhomogeneous acids, is then extracted with one or more alkylphenols (AP)in a reaction vessel 12. The AP is not soluble with the aqueoussolution, so the extraction yields a biphasic system—an upper organiclayer in vessel 12 (containing AP and LA) and a lower aqueous layercontaining LA and any homogeneous acid used in cellulose deconstruction(sulfuric acid, SA, as an exemplary embodiment in FIG. 1A) and lignin34. Alternatively lignin and residual solids produced duringdeconstruction (e.g., humins) can be removed before the liquid-liquidextraction, for example, by simple filtration. As noted above, the LApartitions preferentially into the AP, while any acid, lignin andun-reacted cellulose remain in the aqueous phase. The aqueous solutioncan be recycled via conduit 20 into vessel 10 to be used to deconstructadditional incoming biomass.

The LA/AP solution is then transferred via conduit 22 to separator 16where the LA is separated from the AP. The LA is removed from theseparator 16 via conduit 32, while the AP is recycled from the separator16 back into reactor 12 via conduit 24.

The separator 16 may be any separator now known or developed in thefuture which is dimensioned and configured to separate two or moreliquids from one another. Explicitly included within the word“separator” are distillation columns of any and all description,including batch and continuous distillation columns, in any format,e.g., simple, fractional, steam, vacuum, and short-path distillationcolumns.

As noted in the definitions, the preferred APs for use in the methodinclude one or two alkyl groups that are linear or branched, andgenerally have six or fewer carbon atoms. (Note that these are just thepreferred APs; other may be used and are explicitly within the scope ofthe method.) LA partition coefficients and boiling points for the mostpreferred APs are shown in Table 1. (The values were generated using a50/50 wt % solution of the stated AP and water containing 2M LA, 2Mformic acid, and 0.5 H₂SO₄.)

TABLE 1 Partition Coeff. M/M AP Boiling Point (% of LA in org. phase) (°C.)

2.66 (82%) 224

1.94 (78%) 228

1.15 (70%) 245

 1.1 (70%) 265

 0.8 (60%) 280

 0.4 (40%) 310

0.36 (30%) 334 (The % value in parenthesis is the percentage of thetotal LA detected in the organic phase after the extraction.)Biomass to Gamma-Valerolactone:

FIG. 1B is a schematic illustration of another version of the method inwhich the LA formed as shown in FIG. 1A is further reacted(hydrogenated) over a catalyst in the presence of H₂ to yield GVL. Inthe same fashion as in FIG. 1A, in FIG. 1B a biomass feedstock 8,containing lignocellulose, cellulose, or sugars resulting from theirde-polymerization is introduced into a reaction vessel 10 containing anaqueous solution. The solution in vessel 10 degrades and deconstructsthe cellulose found in the feedstock 8 to yield LA. The digested,aqueous solution containing LA is then extracted with one or morealkylphenols (AP) in a reaction vessel 12. The AP is not soluble withthe aqueous reaction solution, so the extraction yields a biphasicsystem—an upper organic layer in vessel 12 (containing AP and LA) and alower aqueous layer containing unreacted cellulose, any homogeneous orsolid acids, and lignin. The LA partitions preferentially into the AP,while any acids, lignin and any un-reacted cellulose remain in theaqueous phase. The aqueous solution can be recycled via conduit 20 intovessel 10 to be used to deconstruct additional incoming biomass.

In FIG. 1B, rather than separating the LA as a final product, the LA/APsolution is passed via conduit 22 into hydrogenation reactor 14.Hydrogen is supplied to the reactor 14 from an external source (notshown) via conduit 36 or, alternatively, the formic acid co-producedwith levulinic acid can be use as internal source of hydrogen. In thereactor 14, the LA is hydrogenated to yield GVL. It is preferred thatthe hydrogenation reaction take place over a metallic hydrogenationcatalyst, preferably a catalyst comprising ruthenium and tin on asupport. See the definitions, herein, for other catalysts than can beused in the method.

At this point, the method may branch, if desired. In one version of themethod, the entire bulk of the hydrogenated product exiting reactor 14,which comprises GVL may be passed directly into separator 16 via conduit40. The GVL is removed from the separator 16 via conduit 30, while theAP is recycled from the separator 16 back into vessel 12 via conduit 24.(In the same fashion as FIG. 1A, the separator 16 may be any separatornow known or developed in the future which is dimensioned and configuredto separate two or more liquids from one another.)

Alternatively, the effluent from reactor 14 or a portion of the effluentfrom reactor 14 may be returned to vessel 12 via conduit 26. This servesto increase the concentration of GVL within the top, organic phaseinside the vessel 12. This is because GVL partitions extremely favorablyinto the AP extracting solvent from the aqueous reaction solution usedto deconstruct the biomass feed stock. For example, when the AP used forextraction in vessel 12 is sec-butylphenol, the partition coefficientfor LA is 1.94 at 25° C. The partition coefficient for GVL at the sametemperature is 22. Thus, the vast majority of the GVL recycled intovessel 12 via conduit 26, as well most of the newly formed LA enteringvessel 12 via conduit 20 efficiently partitions into the upper, organicAP phase. By cycling the GVL through reactor 12 multiple times, theultimate effluent passed from reactor 14 via conduit 40 into separator16 can be greatly enriched in GVL. That makes the separation of the GVLfrom AP extraction solvent more efficient and economical.

More specifically, in the cellulose deconstruction step depicted in FIG.1B, vessel 10, LA is produced in equimolar amounts with formic acid (FA)(23). Depending on the amount of cellulose added to the aqueous acidicsolution, typically by stepwise addition, the LA concentration in vessel10 can be increased to 5-10 wt % (17). An AP solvent is then added toextract LA and FA without extracting the strong acid (included in thisexample) in vessel 12 (sulfuric acid as shown in FIG. 1B). The data inTable 2 show that as the concentrations of LA and FA in the aqueousphase increase (entries 1-3), the partition coefficient for extractionof LA by the AP in 12 remains at a value of approximately 2 (when using2-sec-butylphenol (SBP) as the AP), while the partition coefficient forextraction of FA increases, although remaining at low values such thatmost of the FA remains in the aqueous phase. Using equal masses oforganic and aqueous phases, the organic phase extracts approximately71-78% of the LA, while extracting only 2-13% of the FA. The LApartition coefficient decreases to 1.2 when using n-pentylphenol as theAP (NPP; entry 4) and to 0.8 when using n-hexylphenol as the AP (NHP;entry 5), while the FA partition coefficient does not changesignificantly.

TABLE 2 Partition coefficients using 4 g of aqueous phase (0.5M H₂SO₄)and 4 g of AP at 298 K. Aqueous Organic Total amount Partition phasephase in organic coefficient (M) (g) phase (%) (C_(ORG)/C_(AQ)) Entry LAFA GVL AP^(‡) LA FA GVL LA FA GVL  1 0.3 0.3 — B 71 2 — 2.0 0.02 —  2 11 — B 73 5 — 2.0 0.05 —  3 2 2 — B 78 13 — 1.9 0.1 —  4 2 2 — P 70 22 —1.2 0.1 —  5 2 2 — H 61 21 — 0.8 0.1  6 2* — B — — 96 — — 22.0  7 2* — P— — 95 — — 10.4  8 2* — H — — 92 — — 7.8  9 2 2 2 B 61 23 93 0.7 0.1 6.310 2 2 4 B 66 43 92 0.6 0.2 4.0 11 2 2 4 P 68 55 89 0.7 0.4 2.6 12 2 2 4H 61 50 87 0.5 0.3 2.3 13 2 4 4 B 68 50 92 0.6 0.3 3.3 14^(†) 2 2 4 B 6850 92 0.6 0.3 3.5 *Aqueous phase is 2M GVL 0.5M H₂SO₄. ^(†)at 353 K.^(‡)B = 2-sec-butylphenol; P = 4-n-pentylphenol; H = 4-n-hexylphenol

Hydrogenation of LA to GVL leads to a decrease in the normal boilingpoint (from 516 to 479 K), such that GVL is more volatile than SBP (500K), NPP (538 K), and NHP (560 K). Thus, GVL will be removed from the APsolvent at the top of the distillation column 16, eliminating the needto evaporate the solvent. As the boiling point of the AP solventincreases, the separation of GVL from the solvent requires fewer platesand lower reflux ratios (22). Furthermore, for all AP solventsinvestigated, the partition coefficient of GVL is higher than for LA(entries 6-8), allowing for the GVL concentration to be increased bysuccessive recycle steps after hydrogenation, as shown in FIG. 1B.However, as the amount of GVL added in the SBP organic phase increases(entries 9 and 10), the LA partition coefficient decreases, such thatthe organic phase extracted 66% of the LA when a 50/50 mixture of GVLand SBP was used, as compared to 78% extraction of LA when GVL was notpresent (entry 3). Similar results were obtained with the other APsolvents tested (entries 11 and 12). Thus, the extent of solvent recycleprior to distillation represents a compromise between achieving highconcentrations of GVL, while also maintaining a high partitioncoefficient for LA extraction.

Another effect of GVL being present in the organic phase in vessel 12 isthat the FA partition coefficient increases slightly, but remains lowerthan the partition coefficient for LA and GVL, suggesting that the FAconcentration in solution will increase relative to the LA concentrationwith repeated recycling of the aqueous solution for cellulosedeconstruction. Entry 13 in Table 2 shows that a higher FA concentrationdoes not affect the partition coefficients. In the absence of otherroutes for FA removal, the amounts of FA and LA extracted will becomecomparable, thus allowing the FA to be used as an internal source of H₂for the reduction of LA to GVL (7).

Another advantage of the high boiling point of the AP solvent is thatthe extraction can be carried out at elevated temperatures (entry 14),suggesting that the processes presented in FIGS. 1A and 1B can becarried out at the temperatures employed for cellulose deconstruction(e.g., about 420 K), thereby decreasing the need for heat exchangers.This results in energy and equipment savings. In addition, sulfuric acidwas not detected in the organic phase for any of the entries in Table 2.Thus, the aqueous phase containing 0.5 M H₂SO₄ can be used for multiplesteps of cellulose deconstruction.

After extracting the LA, the next step in the process outlined in FIG.1B is to reduce LA to GVL. Previous literature has reported thatruthenium on carbon (Ru/C) is an effective catalyst for converting LA toGVL (10, 11); however, the Ru/C catalyst hydrogenated the C═C bonds inSBP, leading to formation of butyl-cyclohexanone (corresponding to 0.3%conversion of SBP; see Table 3, entry 1). In addition, the Ru/C catalystundergoes deactivation with time-on-stream in the presence of FA. Asshown in Table 3, the conversion of LA was only 27% and the GVLselectivity was 90.5% over the Ru/C catalyst after 100 h time-on-stream.So while this catalyst will work in the present method, it is notpreferred. The LA conversion continues to decrease thereafter. Similarbehavior was observed for FA, which is converted to H₂ and CO₂ (24),such that the FA conversion decreased continuously with time-on-stream(70% conversion at 100 h on-stream). Another limitation of the Ru/Ccatalyst is that the selectivity for conversion of FA to CO₂ is only 75%because of CO methanation reactions (25).

TABLE 3 Effect of temperature and feed composition on LA conversionusing Ru—Sn/C with a molar ratio of 3.6:1 Ru:Sn (unless noted) in a flowreactor. Feed (M in SBP) WHSV LA conversion GVL rate LA selectivity (%)Entry LA FA T (K) (h⁻¹) (%) (mmol min⁻¹ g_(cat) ⁻¹) GVL MTHF Other 1* 22 493 2.8 27 0.10 90.5 0.3 9.2 2 2 2 493 1.5 46 0.09 93.4 4.3 2.3 3 2 2513 1.2 58 0.09 88.5 5.5 6.0 4 2 2 473 1.2 19 0.03 91.0 1.4 6.8 5 0.50.5 493 1.2 54 0.09 97.7 0.8 1.5 6 2 0 493 2.2 98 0.30 95.8 3.6 0.6 7 20 473 2.2 52 0.16 97.5 2.5 0 8^(†) 2 2 493 1.5 44 0.09 92.9 4.6 2.5*Catalyst 5% Ru/C. ^(†)feed includes 2M GVL

To modify the selectivity of the catalyst to hydrogenate the C═Ofunctional group in LA versus the C═C bonds in SBP, tin was added to the5 wt % Ru/C in a 3.6:1 Ru:Sn molar ratio. (See the Examples.) Theaddition of Sn eliminated the reduction of SBP for all conditionsstudied in Table 3 and increased the FA selectivity (>99%) to H₂ (26)and CO₂. Furthermore, addition of Sn improved catalyst stability, suchthat the catalyst undergoes slow deactivation over the first 100 h, butthen achieves stable performance for more than 230 h with 46% LA andgreater than 90% FA conversion (Table 3, entry 2). Moreover, addition ofSn did not negatively affect the GVL production rate, and improved theGVL selectivity by minimizing formation of by-products. Increasing thetemperature (entry 3) increased the LA conversion, but decreased theselectivity to GVL, such that the rate of GVL production remainedconstant.

Decreasing the temperature (Table 3, entry 4) decreased the rate of GVLproduction, with minimal effect on selectivity. Decreasing the LA and FAconcentrations (entry 5) did not significantly affect the GVL productionrate, indicating that the rates are of low order with respect toreactant concentrations. The rate of LA conversion is inhibited by thepresence of FA, decreasing from 0.30 to 0.09 mmol min⁻¹ g_(cat) ⁻¹ uponaddition of FA at 493 K (entries 6 and 2), and decreasing from 0.16 to0.03 mmol min⁻¹ g_(cat) ⁻¹ at 473 K (entry 7 and 4). At bothtemperatures, the GVL selectivity remained high. Increasing the GVLconcentration by successive recycle steps did not affect the GVLproduction rate. Entry 8 of Table 3 shows that 2 M GVL in the feed didnot alter the GVL production rate and only slightly increased the rateof methyltetrahydrofuran (MTHF) production. Therefore, an organicsolvent comprising an AP as defined herein and GVL can be used toextract LA without complications in the hydrogenation reactor.

For a commercial process, impurities arising from the deconstruction ofreal biomass may affect the performance of the catalyst used to reduceLA to GVL. FIGS. 2A and 2B show that the rate of GVL production over theRuSn/C catalyst decreased upon changing from a simulated feed to feedsprepared by contacting SBP with aqueous solutions of LA prepared bycellulose degradation of pure cellulose (Sigma-Aldrich), untreated cornstover, and corn stover pre-treated for hemicellulose removal (22, 27).The rate of GVL production from a feed prepared from cellulose was 0.06mmol min⁻¹ g_(cat) ⁻¹, corresponding to 70% of the rate measured for thesimulated feed. The catalyst recovered 100% of its activity when thefeed was changed back to the simulated feed, indicating that thecatalyst did not undergo irreversible deactivation during exposure tothe cellulose-derived feed. At this point, the RuSn/C catalyst had beenused for the production of GVL for more than 300 h (FIG. 2A).

The inlet to the hydrogenation reactor was then switched to a feedprepared from untreated corn stover and extracted with SBP, and the GVLproduction rate decreased to 30% of the rate measured for the simulatedfeed (0.03 mmol min⁻¹ g_(cat) ⁻¹). Importantly, the rate of GVLformation was stable versus time on stream for this stover-derived feed(FIG. 2A), and approximately 60% of the initial activity was recoveredafter changing back to simulated feed. In another experiment, thesimulated feed was changed to a pre-treated corn stover feed (22), andthe rate of GVL production decreased to 45% of the rate of the simulatedfeed (0.04 mmol min⁻¹ g_(cat) ⁻¹; FIG. 2B). After returning to thesimulated feed, 65% of the initial activity was recovered. While itappears that impurities in the feed derived from corn stover affectcatalyst performance, the pre-treatment to remove hemicellulose hadlittle effect on the GVL production rate, indicating that thehemicellulose fraction can be separated to be processed more effectively(e.g., production of furfural and/or other C₅ derivatives).

As outlined in FIG. 1B, the aqueous solution of sulphuric acid and theAP solvent can be recycled to increase the concentration of GVL in thesolvent. This process was simulated by conducting four recycle steps(22). The LA yield from each of the successive cellulose deconstructionsteps ranged from 46-55% during the four cycles; thus showing that theaqueous solution of sulphuric acid can be recycled without furtherpurification. The consistent yield for each of the cellulosedeconstruction steps also demonstrates that the LA remaining in theaqueous phase was inert in the cellulose deconstruction reactor (17).Importantly, the AP solvent (SBP in these examples) extracted 69-75% ofthe LA, and 11-18% of the FA in each of the 4 cycles. The accumulatingGVL did not undergo further reaction during subsequent cycles over theRuSn/C catalyst. The FA yield during cellulose deconstruction decreasedfrom the first to subsequent cycles, suggesting that FA may undergodecomposition during this step.

The GVL concentration in the SBP solvent was 0.46 M after the firstcycle of cellulose deconstruction, extraction, and hydrogenation. Uponcompletion of four such cycles, the GVL concentration increased to 1.44M. For each cycle, greater than 97% of the GVL remains in the organicphase after contacting the aqueous solution from cellulosedeconstruction with the solvent. The GVL that transfers into the aqueousphase remained low for each cycle (<0.03 M) and was stable during thecellulose deconstruction. In agreement with the data in Table 2, theincrease in the GVL concentration in SBP with each cycle decreased theamount of LA extracted during the cycle (see Table 3). However, theeffect is small and does not decrease the overall yield of LA. The costof recycling this LA is minor compared to the decrease in thedistillation column size and operating cost resulting from the overallincrease in the final GVL concentration before the distillation unit(22).

The method described herein using an AP solvent offers significantadvantages in the production of pure and sulfur-free GVL frombiomass-derived cellulose, a required chemical to make fuels andchemicals in other downstream strategies (5, 13). The method describedherein solves two important issues associated with the production of GVLfrom biomass: First, the process achieves effective recycle of themineral acid catalyst used for biomass deconstruction; and second, theprocess achieves a high final concentration of GVL, leading toenergy-efficient recovery/purification of the product (GVL).

TABLE 4 GVL concentration after successive cellulose deconstructionreactions, extractions, and hydrogenations in a batch reactor. CelluloseLiquid extraction deconstruction amount in the Final product yield (%)organic phase (%) in SBP (M) Entry LA FA LA FA GVL GVL 10 1 55 55 75 11— 0.46 2 51 39 73 17 98 0.75 3 49 35 72 18 97 1.01 4 46 27 69 16 97 1.44Any number of types of hydrogenation catalysts can be used in the methodto accomplish the reduction of LA to GVL. Table 5 shows the results ofhydrogenation reactions, LA to GVL, using SBP as the AP, at variousreaction temperatures, and using different hydrogenation catalysts.

TABLE 5 Hydrogenation of LA to GVL in the presence of SBP. 1,4- LA GVLMTHF pentanediol SBP WHSV conv. selectivity selectivity selectivityhydrogenation Catalyst T (C.) (h−1) (%) (%) (%) (%) (%) Topsoe 150 0.5921 100 0 0 0 Topsoe 180 0.59 46 99.6 0.4 0 0 Raney Cu 200 1.13 95 99.50.1 0.4 0 Raney Cu 200 1.13 15 99.9 0.1 0 0 Ru/C 150 0.6 97 98.2 0.2 1.641 Ru/C 150 1.1 18 99.3 0.7 0 0.6 3.6Ru1Cu 150 0.6 22 99.5 0.5 0 0.33.6Ru1Sn 150 0.6 22 99.7 0.3 0 0 3.6Ru1Sn 170 0.6 43 99.4 0.6 0 03.6Ru1Sn 220 1.3 44 97.5 2.5 0 0 3.6Ru1Sn 240 1.3 42 95.5 4.5 0 0

Another approach for converting LA to GVL is via hydrogen transfer,which is depicted schematically in FIG. 1C, where the left-hand side ofthe process is the same as depicted in FIG. 1A. As shown in FIG. 1C, abiomass feedstock 8 is introduced into a reaction vessel 10 containingan acidic aqueous solution. The digested, aqueous, acidic solutioncontaining LA is then extracted with one or more alkylphenols (AP) in areaction vessel 12. The AP is not soluble with the aqueous acidicreaction solution, so the extraction yields a biphasic system—an upperorganic layer in vessel 12 (containing AP and LA) and a lower aqueous,acidic layer containing the acid (sulfuric acid, SA, as an exemplaryembodiment in FIG. 1C) and lignin 34. As noted above, the LA partitionspreferentially into the AP, while the acid, lignin and un-reactedcellulose remain in the aqueous phase. The aqueous acid solution can berecycled via conduit 20 into vessel 10 to be used to deconstructadditional incoming biomass.

In vessel 40, the LA is esterified to produce the LA ester using an acidcatalyst. Once the ester is produced, it is converted into GVL byhydrogen transfer in reactor 44, preferably using a metal oxidecatalyst.

LA can be hydrogenated by hydrogen transfer using a solid oxide catalystand a hydrogen donor such as 2-butanol. (See above for other catalystsfor hydrogen transfer.) Alternatively, to increase catalyst stabilityand maximize yields in transfer hydrogenation, the LA can be transferredto vessel 40, to generate LA esters (i.e., levulinate esters) in thepresence of alcohols or olefins. The ester can be made using homogeneousor heterogeneous catalysts. In the case of heterogeneous catalysts therewill be two phases; in the case of homogeneous catalysts there will beonly one phase as alcohols and olefins are soluble in AP. If theesterification of the LA is carried out using the same or a similarsolution that was used for the cellulose deconstruction, the reactionresults in a biphasic system in which the lower, aqueous phase in vessel40 contains water, alcohol, and the strong acid used to produce theester, and the upper, organic layer contains levulinate esters, alcohol,and AP. (As shown in FIG. 1C, the alcohol is 2-butanol, and thus theresulting LA ester is butyl levulinate (BL).) The water/alcohol/acidsolution can be recirculated via conduit 48 for repeated esterificationof levulinic acid. The upper layer containing the LA esters and AP istransferred via conduit 42 to reactor 44. Reactor 44 preferably containsa solid oxide catalyst, such as zirconia, alumina, magnesia, titania,etc. that converts the LA esters to GVL by hydrogen transfer in thepresence of a hydrogen donor such as 2-butanol. (See the above for othercatalysts for hydrogen trasnfer.) The GVL so formed is transferred viaconduit 46 to separator 16 of isolation of the LA (as describedpreviously). As described previously, the AP may be recycled via conduit24 into reaction vessel 12. As shown in Table 6, overall yield (LA toGVL) can be quite high using different combinations of alcohol transferagents and APs:

TABLE 6 Hydrogen Transfer - LA Esters to GVL Ester or H LA GVL GVL H Hdonor:SBP Time Catalyst:ester conversion yield formation rate donoracceptor (g:g) (h) or LA (g:g) (%) (%)* (μmolg⁻¹min⁻¹) IPA EL 18:1  161:2 >99 86 — IPA EL 8:1 16 1:2 >99 84 — IPA EL 1:1 16 1:2 >99 95 — 2BuOHBL 1:1 16 1:2 >99 83 — 2BuOH BL 1:1 8 1:5 60 51 27.2 2BuOH BL 1:1 4 1:530 29 31.5 2-HO BL 1:1 8 1:5 39 17 9.7 IPA LA 1:4 16 1:2 34 7 1.3 IPA LA1:1 16 1:2 69 15 2.7 *Levulinate esters only by-product. EL =ethyllevulinate, BL = butyllevulinate, LA = levulinic acid

EXAMPLES

The following Examples are included solely to provide a more completedisclosure of the method described and claimed herein. The Examples donot limit the scope of the claims in any fashion.

1. Materials and Methods:

1.1. Liquid-Liquid Extractions

1.1.1. Simulated Feed

Liquid-liquid extractions were carried out in 20 mL glass vials.Typically, 4 g of aqueous solution with 0.5 M sulfuric acid(Sigma-Aldrich, St. Louis, Mo., USA, >96%), LA (Sigma-Aldrich, St.Louis, Mo., USA 98%), FA (Sigma-Aldrich, 98-100%) and/or GVL(Sigma-Aldrich, >98%), in the concentrations indicated, plus 4 g of theindicated AP (2-sec-butylphenol (Alfa Aesar, Ward Hill, Mass., USA >98%)4-n-pentylphenol (Sigma-Aldrich, >98%), 4-n-hexylphenol (Acros Organics,Geel, Belgium, 98%) and GVL, when used, were added to the vial andshaken vigorously for one minute. After the two phases separated, theorganic top phase contained SBP, GVL, LA and FA, and the aqueous bottomphase contained water, sulfuric acid, and the remaining GVL, LA and FA.Both phases were separated and weighed. The extractions at 353 K werecarried out by placing the vials in an oil bath. The organic phase wasanalyzed by gas chromatography (Shimadzu GC2010; Shimadzu PrecisionInstruments, Torrance, Calif., USA) with an FID and RTx®-5-brand column(Restek Corp., Bellefonte, Pa., USA), while the aqueous phase wasanalyzed by HPLC (Waters 2695 system; Waters Corporation, Milford,Mass., USA) with a Bio-Rad Aminex®-brand HPX-87H column and a R1410detector (Bio-Rad Laboratories, Inc., Hercules, Calif., USA). Massbalances for all compounds were within 5%. The amount of FA in theorganic phase was calculated by difference of the initial amount and theamount calculated in the aqueous phase.

1.1.2. Feed from Cellulose Deconstruction

The aqueous phase from the cellulose deconstruction reactor was mixedwith an equal mass of fresh SBP in a 500 mL separatory funnel at roomtemperature. The mixture was shaken for 1 min and allowed to settleovernight to allow the phases to separate. For recycle experiments, theorganic phase was transferred to a Parr reactor in which thehydrogenation reaction was carried out using a RuSn/C catalyst. Afterhydrogenation, the solution was filtered to remove the catalyst andtransferred to a 500 mL separatory funnel for a subsequent extraction ofthe recycled aqueous phase from the cellulose deconstruction reaction.Analysis was the same as indicated in section 1.1.1.

1.2. Hydrogenation Reactions

1.2.1. Flow Reactor

Hydrogenation of the LA was carried out in a fixed-bed reactor operatingin an up-flow configuration. The catalyst was placed in a stainlesssteel tubular reactor (6.35 mm OD) and held between two end plugs ofsilica granules and quartz wool. The catalyst was reduced in-situ for 3h at 723 K (1 K min⁻¹) before use. The feed was introduced into thereactor using an HPLC pump (Lab Alliance-brand Series I; ScientificSystem, Inc., State College, Pa., USA). Simulated feeds for catalyticexperiments were prepared by adding commercial LA, FA and GVL to SBP.The flow of H₂ during the reaction (25 cm³(STP)/min) was controlled by amass flow controller (Brooks Instrument, 5850S; Brooks Instrument, Inc.,Hatfield, Pa., USA). The tubular reactor was fitted inside an aluminumblock and placed within an insulated furnace (Applied Test Systems,Butler, Pa., USA). Bed temperature was monitored at the reactor wallusing a Type K thermocouple (Omega Engineering, Inc., Stamford, Conn.,USA) and controlled using a 16A series programmable temperaturecontroller (Love Controls, Inc., Michigan City, Ind., USA). Reactorpressure (35 bar of H₂) was controlled using a back pressure regulator(model BP-60; GO Regulator, Inc, Spartanburg, S.C., USA). The reactoreffluent flowed into a vapor-liquid separator wherein the liquid productwas collected. Gas phase products were analyzed using an in-line pair ofgas chromatographs. A GC-2014 (Shimadzu) equipped with an FID was usedfor analysis of hydrocarbon products in the gas phase, while CO and CO₂were quantified using a GC-8A (Shimadzu) with a TCD using helium as acarrier/reference. Liquid samples were drained from the separator andthe concentration of organic species quantified using a GC-2010(Shimadzu) with an FID. Identification of products was achieved usingGC-MS analysis (Shimadzu GCQP-2010). Total and individual mass balancesfor each compound were within 5%.

1.2.2. Batch Reactor

A 450 mL Parr Instruments Hastelloy C-276 batch reactor (Parr InstrumentCompany, Moline, Ill., USA), equipped with a variable speed mechanicalstirrer, was loaded with 4 g of reduced and passivated Ru—Sn/C catalystand the organic phase coming from the liquid-liquid separation stepdescribed in section 1.1. The system was purged with helium, pressurizedto 24 bar with H₂ and heated to 453 K (9 K min⁻¹ ramp) with ahigh-temperature fabric heating mantle to reach a final pressure of 35bar of H₂. The reactor was maintained at 453 K overnight while stirringat 600 rpm. At the end of the reaction, the reactor was cooled andweighed. A liquid sample was collected, filtered with a 0.2 μm membrane(Corning, Inc., Corning, N.Y., USA), and analyzed by GC (Shimadzu GC2010with an FID and RTx®-brand-5 column). For the recycling experiments, theorganic phase was transferred to a 500 mL separatory funnel for asubsequent extraction of more LA.

1.3. Cellulose Deconstruction

1.3.1. Microcrystalline Cellulose

For the first cycle, 180 mL of 0.5 M sulfuric acid solution(Sigma-Aldrich) and 7.7 wt % microcrystalline cellulose (5% moisture,average size 20 μm, Sigma-Aldrich) were added to the 450 mL Parr reactor(section 1.2.2). The reactor was purged with helium gas three times andheated to 428 K (9 K min⁻¹ ramp) with a high-temperature fabric heatingmantle. The reactor was maintained at 428 K for 6 h while stirring at600 rpm. At the end of the reaction time, the heating mantle wasremoved, and the built-in cooling line cooled the reactor. The reactorwas weighed, and another dose of cellulose (equal to the first addition)was added. The vessel was resealed and a second cycle started. Afterthree cycles, the mixture was filtered using a 0.2 μm membranedisposable filter system (Corning), and a liquid sample was collectedand analyzed by HPLC (Waters 2695 system with a Bio-Rad Aminex®-brandHPX-87H column and a R1410 detector). The resulting concentration fromthree cycles was 0.68 M LA and 0.69 M FA. For the recycling process,additional degradation cycles were completed with the aqueous solutionremaining from the previous separation step.

1.3.2. Corn Stover

Dried corn stover was obtained through the Great Lakes BioenergyResearch Center, Madison, Wis., USA. Approximately 20 g of dry cornstover and 270 mL of 0.5 M sulfuric acid, which results in anapproximately 2.5 wt % cellulose solution, were added to the 450 mL Parrreactor (section 1.2.2). The corn stover was then deconstructed andanalyzed as indicated in section 1.3.1. The resulting concentrationafter three cycles was 0.25 M LA and 0.37 M FA.

1.3.3. Pretreated Corn Stover

A 5 to 5.5 wt % solids mixture of corn stover and 0.05 M sulfuric acidwas added to the 450 mL Parr reactor in accord with previously publishedmethods (24). The reactor was purged 3 times with helium, heated to 433K in 20 min, and held at 433 K for an additional 20 min. The reactor wascooled using an inline water cooling line and blowing air. The reactorwas weighed, the contents filtered, and the aqueous phase analyzed byHPLC (Waters 2695 system with a Bio-Rad Aminex®-brand HPX-87H column anda RI410 detector). The remaining solids were dried overnight in a 358 Koven. The solids were then used as the cellulose source fordeconstruction as in section 1.3.1. The resulting concentration fromthree cellulose deconstruction cycles using the pretreated corn stoverwas 0.50 M LA and 0.54 M FA.

1.4. Catalysts

1.4.1. Synthesis

The 5 wt % Ru/C was used as received from the vendor (Sigma-Aldrich).The Ru—Sn/C catalyst was prepared by incipient wetness impregnation ofthe 5 wt % Ru/C catalyst with a solution of SnCl₂·2H₂O, which resultedin a final molar ratio Ru:Sn of 3.6:1. The catalyst was dried at 353 Kfor 2 hours before loading into a flow reactor, or reduced for 3 h at723 K (1 K min⁻¹) and passivated in 2% O₂/He for 3 hours before use in abatch reactor.

1.4.2. Chemisorption

Fresh and spent RuSn/C samples were characterized by volumetrictitration of exposed metal sites with carbon monoxide. Staticchemisorption was carried out using a Micromeritics ASAP 2020(Micromerimetrics Instrument Corp., Norcross, Ga., USA). Prior toanalysis, catalyst samples were outgassed under vacuum at 303 K andsubsequently reduced in flowing H₂ at 723 K (80 cm³(STP)/min H₂, 1.3 Kmin⁻¹ heating rate, 240-min hold). The sample was then evacuated at 723K for 60 min to remove adsorbed H₂ and cooled to 303 K. CO uptake wasmeasured volumetrically at 303 K through sequential doses atincrementing pressures to approximately 10 Torr. The sample was againevacuated at 303 K, and a second CO uptake isotherm was collected.Irreversible adsorption of CO was taken as the difference in uptakebetween the two isotherms, and dispersions were calculated bynormalizing total CO uptake by total metal content (Ru plus Sn).

1.4.3. X-ray Diffraction

X-Ray diffraction (XRD) was used to probe the extent of interactionbetween Ru and Sn on the carbon support. In addition, XRD studiesprovided information regarding metal particle size of fresh and spentcatalysts. Powder diffraction was carried out using a Rigaku Rapid IIlarge area curved imaging plate detector (Rigaku Americas, Inc., TheWoodlands, Tex., USA) with a molybdenum source. Prior to XRD studies,RuSn/C catalysts were prepared according to the methods described insection 1.4.1, reduced in flowing H₂ at 723 K (50 cm³(STP)/min H₂, 1.3 Kmin⁻¹ heating rate, 4 h hold), and subsequently passivated at 298 Kunder O₂/He flow (50 cm³(STP)/min, 2% O₂ in He). Samples were crushed toa uniform particle size and loaded into a 0.5 mm borosilicate capillaryfor analysis.

2. RuSn/C Catalyst:

2.1. Stability

FIGS. 3 and 4 illustrate that the Ru—Sn/C catalyst initially undergoesdeactivation, during which the rate of GVL production and LA conversiondecrease in the first 100 h on stream. The catalyst then remains stablefor more than 200 h. In the case of Ru/C, the catalyst showed continuousdeactivation, with the rates of GVL production and LA conversiondecreasing continuously after 200 h.

2.2. Characterization

In XRD patterns for both fresh and spent RuSn/C, the only observablesignal was attributed to the carbon support. XRD did not reveal thepresence of phases corresponding to metallic Ru, metallic Sn, orRu_(x)Sn_(y) alloys. The absence of signal arising from distinct metalor alloy phases suggests that the metal nanoparticles are highlydispersed (<4 nm) in both fresh and spent samples.

The fresh RuSn/C irreversibly adsorbs 101 μmol-CO g⁻¹, corresponding toa metal dispersion of approximately 16%, which is lower than thatobserved for the original Ru/C (26% dispersion). This result isconsistent with expectations that CO does not adsorb irreversibly onmetallic tin. The CO uptake decreases by nearly an order of magnitude to12 μmol g⁻¹ for the spent RuSn/C catalyst, with an apparent dispersionof 1.9%. A decrease in CO uptake and observed dispersion may beattributed to metal sintering and an increase in average particle size;however, this explanation is not consistent with XRD results, whichshowed that significant growth of the metal particles does not takeplace upon exposure to reaction conditions. Thus, the reduced COadsorption capacity may be attributed to deposition of carbonaceousdeposits on the metal particles and/or enrichment in the surface of themetal particles with Sn.

3. Stream Recycle Results:

3.1. Cellulose Deconstruction

Data for successive cellulose deconstruction reactions can be found inTable 7.

TABLE 7 Initial and final concentrations of LA, FA and GVL and LA and FAyields, resulting from successive cellulose deconstruction reactionsusing recycled SA. Initial Final Yield concentration (M) concentration(M) (%) Entry LA FA GVL LA FA GVL LA FA 1 — — — 0.68 0.69 0 55 55 2 0.190.70 — 0.83 1.19 0 51 39 3 0.26 1.11 <0.05 0.87 1.55 <0.05 49 35 4 0.341.39 <0.05 0.92 1.73 <0.05 46 27As the number of times the aqueous solution was recycled increased, theinitial concentration of LA and FA increased. At higher FAconcentrations, the FA decomposed into CO₂ and H₂, which were detectedusing a GC-8A (Shimadzu) with a TCD using helium as a carrier/reference.

3.2. Extraction

After extraction, the organic phase was transferred to a Parr reactorfor hydrogenation of LA and the aqueous phase containing SA was recycledfor a second cellulose deconstruction. In subsequent cycles, the aqueousphase coming from the cellulose deconstruction reactor was mixed withthe organic phase from the previous hydrogenation step. Therefore, afterthe first hydrogenation step, GVL is present in both the aqueous andorganic streams. Aqueous and organic phases were analyzed as mentionedin section 1.1. Detailed data for these extractions can be found inTable 8.

TABLE 8 Aqueous and organic phase concentrations and percentages of LA,FA and GVL before and after extraction with SBP. Initial aqueous Organicphase phase Initial Final Final Final Final aqueous phase LA FA GVL GVLLA FA GVL LA FA GVL Entry (M) (M) (M) (M) (M) (%) (M) (%) (M) (%) (M)(%) (M) (%) (M) (%) 1 0.68 0.69 0 0 0.42 74.1 0.07 11.4 0 0 0.19 25.90.70 88.6 0 0 2 0.83 1.19 0 0.46 0.46 72.2 0.15 16.8 0.42 97.8 0.26 27.81.11 83.2 0.01 2.2 3 0.87 1.55 0.02 0.75 0.56 71.5 0.22 20.2 0.66 97.50.34 28.5 1.39 79.8 0.03 2.5 4 0.92 1.73 0.03 1.04 0.52 69.4 0.17 15.80.96 96.6 0.40 30.6 1.60 84.2 0.06 3.4

3.3. Hydrogenation of LA

Detailed results for the successive batch hydrogenation reactions of LAcan be found in Table 9. For each batch, fresh catalyst was used (4 g).At these high reaction times (i.e., overnight) using fresh catalyst,some reduction of the SBP was observed. However, the GVL selectivityremained over 97% in all cases.

TABLE 9 LA conversion and selectivities for successive hydrogenationreactions using RuSn/C at 453 K and 35 bar (H₂) overnight. LA SBPconver- hydro- Initial (M) Final (M) sion Selectivity (%) genation EntryLA GVL LA GVL (%) GVL MTHF (%) 1 0.42 0 0 0.46 100 97.0 2.6 0.8 2 0.460.42 0.15 0.75 67.4 97.0 2.0 0.4 3 0.56 0.66 0.14 1.01 74.8 98.6 1.2 1.54 0.52 0.96 0.02 1.44 96.2 97.9 2.1 1.44. Distillation:

In the final step of the process, GVL is separated from the AP,obtaining pure GVL at the top of a distillation column. ASPENPLUS®-brand modeling software (Aspen Technology, Inc., Burlington,Mass., USA) was used to conduct simulations of the distillation columnusing different feed compositions and alkylphenols. FIG. 5 shows theenergy ratio (heat necessary in the reboiler divided by the lowercombustion heat of GVL) as indicative of the operational cost, versusthe number of stages, as indicative of the capital cost, to recover 95%of the GVL with 95 wt % purity from the feed at 298 K and 1 bar.

Increasing the concentration of GVL in the feed from 0.5 M to 2.5 Mconsiderably reduces the number of stages necessary to achieveseparation and the heat required in the reboiler. For example, using 0.5M GVL in SBP as feed and with 22 stages, the energy ratio is 152%,meaning that 52% more energy is required than is provided by thecombustion of the GVL. When the GVL feed concentration is 2.5 M, thenthe energy ratio is only 19%, and 10 stages are required. Similarreductions in reboiler energy requirements are observed using APsolvents with higher boiling points. For example, the energy ratio is10% using para-tert-amylphenol (PTAP) as the solvent, a GVLconcentration of 2.5 M, and 10 stages. Another option to reduce thereboiler heat and the number of stages is to carry out the distillationunder vacuum (0.1 bar), but such operation increases capital andoperating costs.

FIG. 6 shows the simulated decrease in required reboiler heat and numberof stages associated with the deconstruction/extraction/hydrogenationrecycling steps documented herein, illustrating how the size of thecolumn and the energy requirements decrease as the GVL concentrationincreases. For example, after a single cycle, the GVL concentration is0.44 M and 30 stages are necessary to carry out the separation, with anenergy ratio of 78%. After 4 cycles, the GVL concentration has increasedto 1.44 M, and with the same number of stages, the energy ratio is just25%. Additional increases in GVL concentration further reduce the heatrequirements and size of the column. Additional energy saving can beachieved if the distillation column is fed directly from thehydrogenation reactor at 493 K, alleviating the need to heat the streamprior to distillation.

5. GVL Extraction:

In this version of the process, GVL, which is a product of the process,is used as solvent to extract levulinic acid (and formic acid ifpresent) from aqueous solutions. Mixtures of water and GVL are normallymonophasic. If the water contains a certain threshold amount or greaterof a solute (typically a water-soluble salt or water-solublecarbohydrate, such as a mono- di- or trisaccharide), the system becomesbiphasic and most of the levulinic acid partitions into the organicphase. See Table 10. The main advantage of this version of the processis that the extraction solvent (GVL) is also the final product. Thus nopurification is required because levulinic acid can be hydrogenated tomake GVL using metal catalysts, such as Ru or RuSn.

FIG. 7 is a schematic diagram of this version of the process. In a first(optional) step, cellulose is deconstructed to produce levulinic andformic acids using a dilute aqueous solution of a mineral acid (seedefinition above) with a sufficient amount of a dissolved solute in thesolution to yield a biphasic system with GVL. As noted above, the soluteis preferably a salt or a sugar, and most preferably NaCl or fructose.After reaction, GVL is added in a liquid-liquid extractor forming abiphasic system. It has been found that saturated salt systems, 35 wt %NaCl in particular, obtain the highest partition coefficients forlevulinic acid (Table 10) although biphasic systems are formed even at 6wt % NaCl. The top phase is an organic phase rich in GVL and LA, whilethe bottom phase is an aqueous phase rich in mineral acid. This aqueousphase can be recycled to carry out additional cellulose deconstructions.The organic phase is carried to a hydrogenation reactor, where thelevulinic is converted into GVL, preferably using heterogeneouscatalysts (i.e., Ru, RuSn), although any suitable catalytic system willsuffice. The conditions in the reactor and the catalyst can be selectedto not hydrogenate the GVL. The outlet of this reactor is a stream ofGVL that can be used as chemical, or processed to produce fuels asbutene. A portion of the GVL is recycled to the second step forsuccessive extractions.

TABLE 10 Partition coefficients of levulinic and formic acids from abiphasic GVL and aqueous system containing salt or fructose. Unlessotherwise noted, all entries used 4 g of aqueous phase with an equalweight of GVL. FA LA FA % LA % wt % wt % Weight % of aqueous R_(FA)R_(LA) in org in org org org  6% NaCl 1.2 1.5 79.2 82.4 2.3 6.2  8% NaCl1.4 2.1 72.0 79.5 2.4 6.9 13% NaCl 1.5 3.0 68.3 81.2 2.5 7.7 24% NaCl1.5 3.7 63.3 80.6 2.5 8.1 35% NaCl 1.6 4.0 68.5 84.8 2.4 7.6 35% NaCl/2g GVL 1.4 3.2 51.6 71.1 3.5 12.4 35% NaCl/1 g GVL 1.3 2.4 21.6 34.3 4.417.6 27% Fructose 1.4 1.6 62.0 65.9 2.2 6.3 39% Fructose 1.5 2.9 75.085.0 2.3 6.9 53% Fructose/2 g GVL 1.9 3.2 55.6 67.8 2.3 7.8

More specifically, in FIG. 7, a biomass feedstock 8, containinglignocellulose, cellulose, or sugars resulting from theirde-polymerization is introduced into a reaction vessel 10 containing anaqueous acidic solution. The solution in vessel 10 degrades anddeconstructs the cellulose found in the feedstock 8 to yield LA. Thedigested, aqueous solution containing LA is then extracted with GVL in areaction vessel 12. (The separate reactors 10 and 12 are shown forillustration purposes only. The cellulose deconstruction reaction andthe extraction with GVL may take place in a single reactor if desired.)The GVL is not soluble with the aqueous reaction solution, so theextraction yields a biphasic system—an upper organic layer in vessel 12(containing the GVL extraction solvent and extracted LA) and a loweraqueous layer containing unreacted cellulose, any homogeneous or solidacids, and lignin. The LA partitions preferentially into the GVL, whileany acids, lignin and any un-reacted cellulose remain in the aqueousphase. The aqueous solution can be recycled via conduit 20 into vessel10 to be used to deconstruct additional incoming biomass.

In FIG. 7, rather than separating the LA as a final product, the LA/GVLsolution is passed via conduit 22 into hydrogenation reactor 14.Hydrogen is supplied to the reactor 14 from an external source (notshown) via conduit 36 or, alternatively, the formic acid co-producedwith levulinic acid can be used as internal source of hydrogen. Inreactor 14, the LA is hydrogenated to yield GVL. It is preferred thatthe hydrogenation reaction take place over a metallic hydrogenationcatalyst, preferably a catalyst comprising ruthenium and tin on asupport. See the definitions, herein, for other catalysts than can beused in the method.

At this point, the method may branch, if desired. In one version of themethod, the entire bulk of the hydrogenated product exiting reactor 14,which comprises GVL may be passed directly to downstream processing orisolated as the final product via conduit 40. (Downstream processing isexemplified in FIG. 7 by producing butene from the GVL. This is just anexemplary downstream product. Many others are possible.)

Alternatively, the effluent from reactor 14 or a portion of the effluentfrom reactor 14 may be returned to vessel 12 via conduits 38 and 26.This serves to increase the concentration of GVL within the top, organicphase inside the vessel 12, which increases the extraction of LA fromthe lower, aqueous phase.

The cellulose deconstruction step with the salt present results in ashorter time to achieve equal levulinic acid yields than without saltpresent. In the case of 0.5 M sulfuric acid, after 1 h reaction time thelevulinic yield without salt present was 45% versus near 60% with thesalt present. Typical levulinic acid yields using a salt-saturated,aqueous acid solution are similar to those obtained without salt present(approximately 55-70%). A saturated salt solution with no acid resultedin a levulinic yield of less than 2%.

Once the deconstruction is completed, the solution is filtered to removesolids. To extract the levulinic acid, GVL is added to the aqueoussolution and results in the previously mentioned partition coefficients(Table 10). Using less GVL (higher aqueous to organic ratio) results ina lower partition coefficient for levulinic acid, but the concentrationof levulinic in the organic layer increases (LA wt % org). This allowsfor having a higher concentration of levulinic going into thehydrogenation reactor. The separation of the phases is spontaneous andoccurs in seconds, leaving two clear phases. Table 10 indicates thepartition coefficient of levulinic and formic acids at differentconditions.

Alternatively, the GVL may be added during the cellulose deconstructionreaction, thereby extracting the levulinic acid as it is produced. Inthis case, lignin, cellulose, and any humins produced during thereaction are dissolved so there is no need for a filtration step toremove the solids. In this approach the yields of LA obtained aresimilar to those obtained without the GVL being present (55-70%), butthe additional chemicals in the product stream may have an adverseimpact on the hydrogenation catalyst. Water can be added to the organicphase to precipitate GVL-soluble lignin; however, the feed would likelyrequire a filtration (or any other solid-liquid separation) step priorto the hydrogenation reactor (14 in FIG. 7) to remove the solids thatwere formed.

After the extraction, the organic phase, rich in GVL and levulinic acidis carried to a hydrogenation reactor (14 in FIG. 7). RuSn is apreferred heterogeneous catalyst which hydrogenates the levulinic acidto GVL without hydrogenating the GVL.

Depending on the amount of GVL and salt added in the previous step someof the mineral acid may partition to the organic phase. The presence ofmineral acid reduces the activity of the catalyst and inhibits thereaction of LA to GVL. See FIG. 8. When the HCl is removed from thefeed, some of the catalytic activity is recovered. Neutralizing themineral acid (for example, by adding NaOH or an amine) or removing (forexample, by using a small amount of a hydrophobic solvent such astrialkylphenol) results in an extremely stable catalyst system (See FIG.9) and higher reaction rates (Table 11).

TABLE 11 Reaction rates of levulinic acid to GVL using RuSn as thehydrogenation catalyst in different solvents. Solvent Rate (mmol/min g)Water 0.14 SBP 0.07 GVL no HCl 0.04 GVL w/HCl 0.005 GVL neutralized10-20% of initial HCl 0.02 GVL neutralized 50% of initial HCl 0.066. Conversion of Cellulose to Levulinic Acid:

Conversion of cellulose to levulinic acid in biphasic systems wascarried out using mineral acids, such as hydrochloric acid (HCl),containing salt, such as 35 wt % sodium chloride (NaCl), and an organicsolvent comprising gamma-valerolactone (GVL). The GVL was used toextract levulinic acid continuously from the mineral acid and tosolubilize the humins that form. The experiments were carried out in 10mL glass reactors at 155° C. in a pre-heated oil bath using magneticstirring.

In a typical experiment, approximately 4 wt % solid cellulose was addedto the aqueous solution of mineral acid, typically 0.1 M HCl containing35 wt % NaCl. The GVL was added to the glass reactor to reach thedesired mass ratio (aqueous layer (g)/organic layer (g)), which wastypically 1:1 with 2 g aqueous phase and 2 g GVL resulting in an overallcellulose concentration of 2 wt %. The glass reactor was placed in theoil bath, held for a certain time, then taken from the oil bath andcooled with an air line. A small portion of the organic phase wassampled, and then an additional 2 wt % cellulose bolus was added to thereactor and the reactor was run again. The boluses increase theconcentration of levulinic acid in the GVL, which is desired fordownstream processing options, such as distillation or further upgradingreactions. After three (3) boluses, the two phases were then separatedand both analyzed to quantify the levulinic acid, formic acid, glucose,and GVL using an HPLC.

Levulinic acid yields for experiments with 2 wt % cellulose, boluses,and different acid concentrations at 155° C. are shown in Table 12. Themass ratio of aqueous solution to GVL was kept at 1 for theseexperiments by using 2 g aqueous solution with 2 g GVL. For all cases,75% of levulinic acid was retained in the GVL due to the partitioncoefficient of levulinic acid (ratio of the levulinic acid concentrationin GVL divided by the levulinic concentration in the aqueous phase)being equal to approximately 4. The maximum yield of levulinic acidachieved was 72% after 1 bolus, and after 3 boluses, the overalllevulinic acid yield was approximately 50-55%. In all experiments, nosolids remained due to their solubility in GVL.

TABLE 12 Results of cellulose deconstruction experiments carried out at155° C. in a biphasic system, using GVL as the organic solvent and amineral acid containing 35 wt % NaCl in a 1:1 ratio. 1^(st) bolus 2^(nd)bolus 3^(rd) bolus Levulinic Levulinic Levulinic Cellulose Time acidCellulose Time acid Cellulose Time acid Catalyst wt. % (h) yield (%) wt.% (h) yield (%) wt. % (h) yield (%) 0.1M 2.11 4 66 1.87 5.1 53 2.85 4 50HCl 0.25M 1.84 1.25 63 1.89 2 54 2.03 1.5 50 HCl 0.75M 1.90 1.6 71 2.361.5 64 2.01 1.34 55 HCl 1.25M 1.98 1.5 72 2.25 1.5 60 1.99 1.34 55 HCl7. Conversion of Corn Stover to Furfural and Levulinic Acid:

Corn stover contains both hemicellulose and cellulose, which primarilycontain xylose and glucose, respectively. Therefore, the hemicellulosecan be deconstructed using acid hydrolysis to xylose, which can furtherbe dehydrated to furfural. The cellulose can be deconstructed tolevulinic acid in a second acid hydrolysis step. In addition, both thehemicellulose and cellulose deconstructions can occur in the same stepdepending on the process economics.

For the two-step process, conversion of hemicellulose to furfural in abiphasic reactor system was carried out using mineral acids, such ashydrochloric acid (HCl), containing salt, such as 35 wt % sodiumchloride (NaCl), and an organic solvent comprising gamma-valerolactone(GVL). The GVL was used to extract furfural continuously from themineral acid, which inhibits further degradation, and to solubilize thehumins that form and the lignin that comes from the corn stover. Theexperiments were carried out in 10 mL glass reactors at 170° C. in apre-heated oil bath using magnetic stirring.

In a typical experiment, approximately 7-10 wt % solid biomass was addedto the aqueous solution of mineral acid, typically 0.1 M HCl containing35 wt % NaCl. The GVL was added to the glass reactor to reach thedesired mass ratio (aqueous layer (g)/organic layer (g)), which was 4 gaqueous phase and GVL total, which resulted in an overall corn stoverconcentration of 3.6-5 wt %. The glass reactor was placed in the oilbath, held for a pre-determined time, then taken from the oil bath andcooled with an air line. The glass reactors were then centrifuged, andthe organic phase was then separated and analyzed to quantify thelevulinic acid, formic acid, glucose, xylose, furfural, and GVL andpentenoic acid (which can form by ring-opening of GVL) using an HPLC.Yields of furfural and levulinic acid for experiments are shown in Table13 (entries 1-3). For all cases, 90% of furfural was retained in theGVL. The maximum yield achieved was 74% and the levulinic acid yield wasless than 10%.

An additional layer of GVL, equal to the initial amount, was added tothe remaining aqueous layer and solids. The glass reactor was placed inthe oil bath, held for a pre-determined time, then removed from the oilbath and cooled with an air line. The organic phase was then separated,and both layers were analyzed to quantify the levulinic acid, formicacid, glucose, xylose, furfural, pentenoic acid, and GVL using an HPLC.Furfural and levulinic acid yields for experiments are shown in Table 13(entries 4-6). For all cases, more than 70% of levulinic acid wasretained in the GVL. The maximum levulinic yield was approximately 50%and the furfural yield was less than 15%. No solids remained due totheir solubility in GVL.

For the one-step process, conversion of hemicellulose to furfural andcellulose to levulinic acid occurred in the same step. A biphasicreactor system was used with mineral acids, such as hydrochloric acid(HCl), containing salt, such as 35 wt % sodium chloride (NaCl), and anorganic solvent comprising gamma-valerolactone (GVL). The experimentswere carried out in 10 mL glass reactors at 170° C. in a pre-heated oilbath using magnetic stirring.

In a typical experiment, approximately 10 wt % solid biomass was addedto the aqueous solution of mineral acid, typically 0.1 M HCl containing35 wt % NaCl. The GVL was added to the glass reactor to reach thedesired mass ratio (aqueous layer (g)/organic (g)), which was 4 gaqueous phase and GVL total, which resulted in an overall corn stoverconcentration of 5 wt %. The glass reactor was placed in the oil bath,held for a pre-determined time, then taken from the oil bath and cooledwith an air line. Both phases were then separated and analyzed toquantify the levulinic acid, formic acid, glucose, xylose, furfural,pentenoic acid, and GVL using an HPLC. Furfural yields wereapproximately 40%, and the levulinic acid yields were approximately 60%(Table 13, entry 7). For the one-step process, no solids remained due tothe GVL solubilizing them.

TABLE 13 Results of corn stover deconstruction experiments carried outat 170° C. in a biphasic system, using GVL as the organic solvent and amineral acid containing 35 wt % NaCl. Aqueous: Corn Furfural LevulinicOrganic stover Time yield acid yield Entries Step Catalyst (g/g) wt. %(min) (%) (%) 1 Hemicellulose* 0.1M 1 5.0 15 68 6 HCl 2 Hemicellulose*0.1M 2 5.1 25 74 8 HCl 3 Hemicellulose* 0.25M 1 5.0 10 64 4 HCl 4Cellulose** 0.1M 1 4.3 200 11 48 HCl 5 Cellulose** 0.1M 2 5.0 190 15 48HCl 6 Cellulose** 0.25M 1 5.1 420 13 49 HCl 7 1-step 0.1M 1 4.9 75 39 59HCl *Hemicellulose conversion from corn stover in step (1). **Celluloseconversion in step (2) after removal of hemicellulose from corn stoverin step (1).8. Simultaneous Dehydration of Xylose to Furfural and Decomposition ofGlucose to Levulinic Acid in a Biphasic System with GVL:

Simultaneous conversions of xylose and glucose in aqueous solutions toobtain furfural and levulinic acid were carried out using mineral acids,such as HCl, in the presence of salts, i.e. NaCl. An organic extractingsolvent comprising gamma-valerolactone (GVL) was used to extractfurfural and levulinic acid continuously. The experiments were carriedout in 10 mL glass reactors kept at constant temperature in a pre-heatedoil bath using magnetic stirring. The experiments were carried out at175° C. In a typical experiment, an aqueous solution containing xyloseand glucose with desired weight percentages was prepared to obtain a 0.1M HCl concentration in the NaCl-saturated aqueous solution. The massratio of xylose to glucose was kept at 5 to simulate pre-hydrolysisliquors (PHL) obtained as a side stream in Dissolving Pulp Production.

The aqueous solution and GVL were added into the glass reactor to reachthe desired mass ratio (aqueous layer (g)/GVL (g)). To end thereactions, the glass reactors were taken out from the oil bath andcooled in ice. The two phases were then separated and analyzed toquantify furfural, levulinic acid, glucose, and xylose using GC andHPLC. Xylose/glucose conversion, furfural/levulinic acid yield valuesare shown in Table 14 for experiments with 1.5 wt % xylose and 0.3 wt %glucose feed with 0.1 M HCl (35% NaCl) at 175° C. at times ranging from25-35 min. The mass ratio of aqueous solution to GVL was kept at 1 forthese experiments by using 2 g of aqueous solution with 2 g of GVL. Forall cases 95% of furfural and 86% of levulinic acid are retained in GVL.The maximum yield achieved for furfural was 81% at approximately 30 min.Under these conditions, 81% of glucose was converted with almostquantitative selectivity. Longer times resulted in lower furfural yieldsdue to the degradation of furfural, whereas the glucose conversionincreased with time.

TABLE 14 Results of simultaneous glucose/xylose dehydration experimentscarried out at 175° C. in a biphasic system with 0.1M HCl containing 35wt % NaCl, 1.5 wt % xylose, and 0.3 wt % glucose, using GVL as theextracting solvent in a 1:1 aqueous to organic ratio. Xylose GlucoseFurfural Levulinic Time conversion conversion Yield Acid (min) (%) (%)(%) Yield (%) 25 99 77 81 74 30 99.6 81 81 79 35 100 88 79 86

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What is claimed is:
 1. A method to isolate levulinic acid (LA), themethod comprising: (a) producing an aqueous solution comprising LA bydeconstructing cellulose, hemicellulose, glucose, xylose, oligomersthereof or combinations thereof, in an aqueous, acidic reactionsolution, to yield the aqueous solution comprising LA or an aqueoussolution comprising LA and fufural; and then (b) adding a sufficientconcentration of a water-soluble solute to the aqueous solution of step(a) to yield an aqueous solution that is substantially immiscible withgamma-valerolactone (GVL); and then (c) extracting LA from the aqueoussolution of step (b) using an extraction solvent comprising GVL; whereinthe aqueous solution comprising LA of step (a) is produced in a biphasicsystem having a first phase and a second phase, wherein the first phasecomprises the aqueous, acidic reaction solution and the second phasecomprises GVL, and wherein the first and second phases are substantiallyimmiscible.
 2. The method of claim 1, wherein the aqueous, acidicreaction solution of step (a) comprises an acid selected from the groupconsisting of solid acids, hydrochloric acid, nitric acid, phosphoricacid, sulfuric acid, boric acid, hydrofluoric acid, trifluoroaceticacid, hydrobromic acid, acetic acid, oxalic acid, toluenesulfonic acid,and Lewis acids.
 3. The method of claim 1, wherein the water-solublesolute of step (b) is a water-soluble salt, monosaccharide,disaccharide, or trisaccharide.
 4. The method of claim 3, wherein thewater-soluble solute is sodium chloride or fructose.
 5. The method ofclaim 3, wherein the waters-soluble salt is sodium chloride.
 6. Themethod of claim 5, wherein the sodium chloride is present in aconcentration of from about 6 wt % to about 35 wt % (saturation), basedon the weight of the water in the aqueous solution.
 7. The method ofclaim 1, further comprising, after step (c): (d) converting all or aportion of the extracted LA into GVL.
 8. The method of claim 7, whereinstep (d) comprises converting the LA into GVL in the presence of acatalyst comprising one or more metals from Groups 6-14 of the periodicchart.
 9. The method of claim 7, wherein step (d) comprises convertingthe LA into GVL in the presence of a catalyst comprising ruthenium,nickel, platinum, rhodium, tin, copper, and combinations thereof. 10.The method of claim 9, wherein the catalyst comprises ruthenium and tin.